This project deals with the interactions of tobacco mosaic virus and its components: virus-virus interactions, protein-protein interactions, RNA-RNA interactions, protein-RNA interactions and the interactions of the virus and its components with ions, with organic molecules and with other proteins. Of special concern is the energetics of TMV protein polymerization. Plans for the coming year include an attempt to determine whether the enthalpy change in the polymerization process is essentially constant over the temperature range studied and whether the number of hydrogen ions per A protein molecule involved in the actual equilibrium between 4S and 20S components is different at pH values below 6.3 from that above pH 6.3. It is also planned to resume studies on the polymerization of acetylated TMV protein and protein in which tyrosine 139 is dibrominated. Other plans include specific ion binding studies, especially calcium ion binding by polymerized protein at pH about 5, an investigation of conformational changes associated with virus protein polymerization and an attempt to explain certain peculiarities in the electro-optical behavior of tobacco mosaic virus.